Recently, in keeping with the tendency towards the higher recording density of magnetic recording signals, shorter recording signal wavelengths, narrower recording track widths and higher access speeds to the recording medium have been realized. For this reason, the recent tendency is to use thin-film magnetic head which are compact and which have high frequency characteristics as compared to conventional magnetic heads employing bulk magnetic materials.
In general, as regards the First Aspect, a thin-film magnetic head is constituted by a lower magnetic film formed on a substrate by the interposition of an insulating film, coil conductor layers, a second insulating layer, a gap layer and an upper magnetic film. The thicknesses of these layers or films are of the order of microns and, for further improving the aforementioned properties, an increasing demand is raised towards further reducing the thicknesses of the layers and films.
When the thin-film magnetic head is built into a magnetic storage system and reads or write the magnetic information in the state of being floated above or slidingly contacted with a magnetic recording medium, it may occur frequently that the static electricity generated on the recording medium be transferred towards the magnetic head, or the static electricity be generated between the magnetic recording medium and the magnetic head, as a result of which electrostatic charges tend to be deposited on the electromagnetic transducer units.
If the electromagnetic transducer units are charged electrically in this manner, the electrostatic charges tend to be collected on the lower magnetic film, on account of the specific construction of the electromagnetic transducer units. The electrostatic charges thus collected on the lower magnetic film tends to raise the electrical potential of the lower magnetic film to offer dielectric breakdown to the insulating layer provided between the lower magnetic film and the substrate, the electrostatic charges then reaching the substrate to cause the destruction of the thin-film magnetic head.
It may also occur that static electricity be produced while the head is in transport or temporarily stored by itself in readiness for being mounted in the magnetic storage system. Such static electricity is known to be discharged momentarily on attaching the magnetic head to the magnetic storage system to cause similarly the destruction of the thin-film magnetic head.
In the JP Patent KOKAI Publication No. 1-116910, there is disclosed a thin-film magnetic head capable of preventing the dielectric breakdown of the insulating layer by the static charges collected on the lower magnetic head. With this thin-film magnetic head, shown herein in FIG. 3, a metallic film 14 is provided on a chamfered portion (A) of a surface 12 of the magnetic head opposite to the floating surface of the slider for shorting an insulating layer 33 interposed between the substrate 2 and the lower magnetic film 24 of the electromagnetic transducer unit 9.
As regards the Second Aspect, conventional thin-film magnetic head used for a hard disc apparatus is explained by referring to FIGS. 11 and 12. On a substrates, formed of a magnetic or non-magnetic material, there are step by step formed a lower magnetic film 3 of a soft magnetic material, insulating layer 4 of an organic resist material, a coil conductor layer 5 of an electrically conductive material, such as Cu, and an upper magnetic layer 6 of a soft magnetic material similar to that of the lower magnetic film 3. Between an upper magnetic pole formed by the upper magnetic film 6 and a lower magnetic pole formed by the lower magnetic film 3, there is defined a magnetic gap 7 on the side of a floating surface 21 of the substrate 2 facing a magnetic recording medium, not shown.